Biodegradable PHB-Rubber Copolymer Toughened PLA Green Composites with Ultrahigh Extensibility

The sustainable biopolymer, poly(lactide) (PLA), has been intensely researched over the past decades because of its excellent biodegradability, renewability, and sustainability. The boundless potential of this sustainable biopolymer could resolve the adverse negative impact caused by the petroleum-based polymers. However, the inherent drawback of PLA such as brittleness, low heat distortion temperature, and slow recrystallization rate narrowed the broad applications in biomedical, automotive, and structural fields. In this study, we successfully synthesized a PHB-based filler (PHB-di-rub) displaying synergetic functions of (1) effective nucleation and (2) extreme toughening of the PLA matrix at only 5% (1.5 wt % PHB content). Remarkably, the storage modulus improves by 15%; tensile elongation extends by 57-fold (300% strain) and toughness by 38-fold while maintaining its original strength and stiffness. Likewise, 10% of PHB-di-rub (3 wt % PHB content) has an even higher improvement with a storage modulus improvement by 32%, elongation by 128-fold (680% strain), and toughness by 84-fold, with a marginal change in strength and stiffness. NMR results confirmed the structure of PHB-di-rub, where PHB acts as the rigid core and the poly(lactide-cocaprolactone) (DLA-co-CL) random copolymer confers the flexibility. DSC, WARD, and POM display the excellent nucleating ability of PHB-di-rub. SEM shows the morphology of elongated fibrils structure with strong matrix-filler interaction and homogeneous filler dispersion. SAXS, WAXS, and WARD elucidate the extreme toughening mechanism to be a combination of rubber-induced crazing effect and highly orientated PLA matrix with PHB-di-rub. The Herman's orientation function further quantifies the extreme elongation (680%) owing to the perfect alignment. This highly biodegradable biocomposite with high strength and toughness shows potential in replacing the current petroleum-based polymers, which open up to broader prospects in the biomedical, automotive, and structural application.